Method and apparatus for controlling the washing step in a blood centrifugation cell

ABSTRACT

A method and apparatus for controlling the washing step in a blood centrifugation cell in which washing solution is introduced into the blood centrifugation cell and the cell contains compacted red cells and supernatant at the beginning of the washing step. The apparatus can comprise various sensors and a computer. The sensors sense and transmit to the computer three inputs. The first input is indicative of the total volume of blood that enters the cell during the filling step and the total amount of washing solution that enters the cell during the washing step. The second input is indicative of the hematocrit value of the blood introduced during the filling step. The third input is indicative of the geometric characteristics of the cell. Based on the inputs, the computer executes an algorithm that produces a first output that is the concentration of the supernatant in the supernatant-washing solution mixture.

FIELD OF THE INVENTION

The invention relates to blood centrifuges and in particular relates toa system for controlling the washing step in a blood centrifugationcell.

BACKGROUND OF THE INVENTION

It is known that in some medical procedures, such as inter- andpost-operative autotransfusion, there is the need to separate the plasmafrom the red cells of the blood aspirated from the operating area, so asto make them available for re-infusion to the patient. It is also knownthat currently this procedure is performed in centrifugation cells inwhich the blood is introduced by means of a peristaltic pump.

A centrifugation cell substantially comprises two bells which aremutually coaxial and rigidly coupled, and the portion of space betweenthem is connected to the outside by means of two tubes, an inlet tubeand an outlet tube, which are connected to the bells by means of arotary coupling. The two bells are turned about their own axis, whilethe tubes are kept motionless.

The procedure provides for a first step for filling the cell, in whichthe blood is introduced by means of the inlet tube. Due to thecentrifugal force, the red cells, which are the heaviest cellularcomponents of blood, are propelled outward, compacting against the wallof the outer bell. Other cellular components such as white blood cellsand platelets are arranged in a thin layer known as buffy coat directlyadjacent to the mass of compacted red blood cells. The separated plasma,the remaining component of blood, is arranged in a layer which liesabove the buffy coat. The plasma, which contains various substances suchas anticoagulant, free hemoglobin and other substances from theoperating field, will be referenced hereinafter as “supernatant”.

As filling continues, the buffy coat moves closer to the rotation axis,displacing the supernatant toward the outlet tube of the cell. When thesupernatant reaches the outlet tube the supernatant flows out of thecell into an adapted collection bag.

The flow of the supernatant in the outlet tube continues until anoptical detector reports that the buffy coat has reached the outlet tubeof the cell. At this point the filling step has ended and theintroduction of new blood into the cell ends. The cell now containscompacted red cells and supernatant, which must be eliminated since itcannot be re-infused to the patient together with the red cells.

The above-described filling step is followed by a washing step performedby means of a washing solution which, when introduced into the cell,gradually takes the place of the supernatant that is expelled. At theend of the washing step the cell contains red cells and washingsolution, i.e., substances suitable to be re-infused to the patient. Thecontents of the cell are collected in a suitable bag in a third step ofthe procedure, known as emptying.

Our attention is focused exclusively on the washing step, which iscurrently performed in manners that are not entirely satisfactory. Afirst procedure adopted in the background art provides for introducingin the cell a preset amount of washing solution at a value that isassuredly more than sufficient to wash the supernatant. The consequentoversizing, however, wastes time and washing solution.

Another procedure used in the art provides a transparency sensor on theoutlet duct. However, this sensor is not able to detect the passage oftransparent components of the supernatant such as the anticoagulant, andtherefore does not provide entirely satisfactory results.

SUMMARY OF THE INVENTION

The invention provides a system for controlling the washing step inwhich the washing step can be stopped when the intended result isreached. The present invention provides a method for controlling awashing step in a blood centrifugation cell wherein washing solution isintroduced into the blood centrifugation cell in the washing step, thecell containing compacted red blood cells and supernatant at thebeginning of the washing step. The method comprises: (1) providing ablood centrifugation cell, a pump for communicating liquid to the bloodcentrifugation cell, and a computer configured to receive data andproduce at least one output; (2) providing first input data to thecomputer indicative of the total volume of liquid that has entered thecell during the filling step that precedes the washing step and duringthe washing step itself, the liquid being blood during the filling stepand the liquid being washing solution during the washing step; (3)providing second input data to the computer indicative of the hematocritvalue of the blood that was introduced during the filling step; (4)providing third input data to the computer indicative of the geometriccharacteristics of the cell; (5) processing the first, second, and thirdinput data in the computer to produce a first output, said first outputbeing the concentration of the supernatant in the supernatant-washingsolution mixture that is present in the cell during the washing step,said first output being produced by the computer executing an algorithmthat expresses the supernatant extinction law inside the cell using thefirst, second, and third input data; and (6) stopping the washing stepwhen a certain concentration of supernatant in the supernatant-washingsolution is reached.

In addition, the invention provides an apparatus for performing themethod for controlling the washing step in a blood centrifugation cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a blood centrifugation cell.

FIG. 2 is a diagram of an apparatus of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the figures, the reference numeral 1 generallydesignates the blood centrifugation cell, which comprises inner bell 2and outer bell 3, which are mutually rigidly coupled and are made torotate in the direction of the arrow in the figures. The numeral 4respectively designates the inlet tube to the portion of space comprisedbetween the two bells. Peristaltic pump 5 pumps fluids into inlet tube4. The fluids follow path 7 into region 10 between the inner and outerbells. Centrifugation separates blood components, as described furtherbelow, and supernatant flows out of the centrifuge via outlet tube 6.The inlet and outlet tubes are connected to the assembly of the innerand outer bells by means of a rotary coupling, so that they can remainmotionless.

During the cell filling step, the red blood cells enter the cell alongpath 7 due to the action of the peristaltic pump 5, which is connectedat the suction to a container known as a cardiotomy reservoir 15. Duringcentrifugation, the red blood cells are compacted in region 8, and thesupernatant follows path 11 to the outlet tube 6. Buffy coat 9 separatesthe compacted red blood cells from the supernatant in region 10. Thesupernatant then flows toward the outlet tube 6 of the cell along thepath 11.

When buffy coat 9, by moving increasingly closer to the rotation axis,reaches the full level indicated by a sensor, the introduction of bloodinto the cell ceases as pump 5 stops. Now the filling step has ended andcell 1 contains compacted red cells and supernatant.

This is followed by a washing step to eliminate the supernatant by meansof a washing solution. A preferred washing solution is physiologicalsaline solution (0.9 g/L NaCl in water). The washing solution isconveyed to cell 1 through inlet tube 4 by pump 5, which is incommunication with a reservoir of washing solution.

The washing solution gradually takes the place of the supernatant, andat the end of the washing step in cell 1, the replacement of thesupernatant with the washing solution has occurred substantiallycompletely. A minute amount of supernatant in cell 1 remains and will bereinfused to the patient. However, small amounts of supernatant areobviously tolerable.

During the washing step, therefore, in the volume of the cell 1 that isnot occupied by the compacted red cells, there is a mixture ofsupernatant and washing solution. The expression “supernatantconcentration” is used to designate the ratio between the volume ofsupernatant present in said mixture and the total volume of saidmixture, and it is immediately evident that the value of saidconcentration varies during washing from the initial value of 1, whenall the space available is occupied by the supernatant, toward the idealfinal value, which is zero and would be reached if the supernatant wereeliminated completely and fully replaced by the washing solution. Theexpression “supernatant extinction law” is used to designate the lawthat regulates the variation of the concentration of supernatant in thesupernatant-washing solution mixture as it decreases from the initialvalue of 1 toward the final value.

The control system includes sensor 12, which is suitable to provide thehematocrit reading of the blood entering the cell during the fillingstep, encoder or sensor 13 on the driving shaft of the peristaltic pump5, which detects data related to the rotation angles of said shaft, andcomputer 14.

The computer executes an algorithm, derived from a mathematical model orfrom the processing of experimental data, that expresses the supernatantextinction law within cell 1 and has three inputs and one output.

The first input comprises the volume of the liquid that enters the cellduring the filling step, which is blood, and during the washing step,which is washing solution. This first input is provided, in thedescribed embodiment, by the encoder 13. The data it transmits to thecomputer 14 related to the rotation angles gradually covered by the pump5 are converted, since the characteristics of said pump and of the tube4 are known, into data related to the volume of liquid progressivelyconveyed. However, clearly the encoder 13 might be replaced with anyliquid flow measurement instrument.

The second input comprises the hematocrit reading of the blood enteringcell 1 during the filling step, and is provided by sensor 12, whichreports to computer 14 the hematocrit reading of the individual smallvolumes of blood that enter cell 1 continuously. The second input mightbe provided in other forms. For example, the computer 14 could includean operator interface which allows entering into the computer 14 datarelated to the hematocrit value of the blood, which can be determinedfrom the cardiotomy reservoir located at the intake of the pump 5.

The third input comprises the geometric characteristics of the cell.Accordingly, there are means that allow the operator to enter intocomputer 14 data related to these characteristics. Alternatively, asensor 16 could be provided for automatic detection of saidcharacteristics.

On the basis of the three listed inputs, computer 14 provides an outputat each instant of the value of the concentration of supernatant in thesupernatant-washing solution mixture that is present in the cell 1during the washing step. In addition, it is possible to provide time asa fourth input.

The invention includes means that allow stopping the washing step whenthe intended conditions are reached. In the described embodiment thereis the display 14 a, which shows at each instant the value of theconcentration of supernatant and thus allows the operator to interveneand turn off the pump 5 when said value reaches the threshold deemedacceptable. According to a different embodiment, there is a controllerto stop automatically the operation of the pump 5 when saidconcentration reaches the threshold value that is preset as acceptable.

Various modifications and alterations to this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention. It should be understood that thisinvention is not intended to be unduly limited by the illustrativeembodiments and examples set forth herein and that such examples andembodiments are presented by way of example only with the scope of theinvention intended to be limited only by the claims set forth herein asfollows.

1. A method for controlling a washing step in a blood centrifugation cell wherein washing solution is introduced into the blood centrifugation cell in the washing step, the cell containing compacted red blood cells and supernatant at the beginning of the washing step, the method comprising: providing a blood centrifugation cell, a pump for communicating liquid to the blood centrifugation cell, and a computer configured to receive data and produce at least one output; providing first input data to the computer indicative of the total volume of liquid that has entered the cell during the filling step that precedes the washing step and during the washing step itself, the liquid being blood during the filling step and the liquid being washing solution during the washing step; providing second input data to the computer indicative of the hematocrit value of the blood that was introduced during the filling step; providing third input data to the computer indicative of the geometric characteristics of the cell; processing the first, second, and third input data in the computer to produce a first output, said first output being the concentration of the supernatant in the supernatant-washing solution mixture that is present in the cell during the washing step, said first output being produced by the computer executing an algorithm that expresses the supernatant extinction law inside the cell using the first, second, and third input data; and providing an indication when a certain concentration of supernatant in the supernatant-washing solution is reached.
 2. The method of claim 1, wherein the algorithm has time as a fourth input data.
 3. The method of claim 1, wherein the algorithm that expresses the supernatant extinction law inside the cell is derived from a mathematical model.
 4. The method of claim 1, wherein the algorithm that expresses the supernatant extinction law inside the cell is derived from an experimental analysis.
 5. The method of claim 1, wherein the pump is a peristaltic pump comprising on the drive shaft of the pump a sensor suitable to transmit to the computer said first input data related to the rotation angles of said drive shaft.
 6. The method of claim 1, further comprising providing a sensor for measuring the volume of liquid entering the cell and suitable to transmit to the computer said first input data.
 7. The method of claim 1, further comprising providing a sensor for measuring the hematocrit value of the blood entering the cell during the filling step and suitable to transmit to the computer said second input data.
 8. The method of claim 1, further comprising providing an operator interface for entering into the computer said second input data indicative of the hematocrit value of the blood.
 9. The method of claim 8, wherein said pump comprises an intake and a cardiotomy reservoir is located at the intake for said pump, and wherein said data indicative of the hematocrit value of the blood is determined by measuring a hematocrit value of the blood in the cardiotomy reservoir.
 10. The method of claim 1, further comprising providing an operator interface for entering into the computer said third input data indicative of the geometric characteristics of the cell.
 11. The method of claim 1, further comprising providing a sensor for automatically detecting the geometric characteristics of the cell and suitable to transmit to the computer said third input data.
 12. The method of claim 1, further comprising providing an operator interface for displaying the concentration of the supernatant in the supernatant-washing solution mixture.
 13. The method of claim 12, wherein the operator stops the washing step when the certain concentration of supernatant is reached.
 14. The method of claim 1, further comprising providing a controller for stopping the washing step when the certain concentration of supernatant in the supernatant-washing solution is reached.
 15. The method of claim 14, wherein the controller stops the washing step when a preset value of the concentration of supernatant in the supernatant-washing solution mixture is reached.
 16. An apparatus for controlling a washing step in a blood centrifugation cell wherein washing solution is introduced into the blood centrifugation cell in the washing step, the cell containing compacted red blood cells and supernatant at the beginning of the washing step, the apparatus comprising: a pump for communicating liquid to the blood centrifugation cell; a first sensor configured to produce first input data indicative of the total volume of liquid that has entered the cell during the filling step that precedes the washing step and during the washing step itself, the liquid being blood during the filling step and the liquid being washing solution during the washing step; a computer which executes an algorithm that expresses the extinction law of the supernatant inside the cell using said first input data, second input data indicative of the hematocrit value of the blood that was introduced during the filling step, and third input data indicative of the geometric characteristics of the cell, to produce a first output, said first output being the concentration of the supernatant in the supernatant-washing solution mixture; an operator interface for entering input data and displaying said first output data; and means for indicating when a certain concentration of supernatant in the supernatant-washing solution is reached.
 17. The apparatus of claim 16, further comprising a second sensor for measuring the hematocrit value of the blood entering the cell during the filling step and suitable to transmit to the computer said second input data.
 18. The apparatus of claim 16, further comprising a second sensor for automatically detecting the geometric characteristics of the cell and suitable to transmit to the computer said third input data.
 19. The apparatus of claim 16, wherein the pump is a peristaltic pump comprising on the drive shaft of the pump the first sensor suitable to transmit to the computer said first input data related to the rotation angles of said drive shaft.
 20. The apparatus of claim 16, further comprising a second sensor for measuring the volume of liquid entering the cell and suitable to transmit to the computer said first input data. 